Burgess Shale

Hallucigenia sparsa (an onychophoran)

When originally discovered and prepared, fossils of the animal Hallucigenia appeared to have preserved two rows of spines on one side of the animal and one row of tentacles on the other. Identifying its head was a problem - the fossil showed only a rounded, dark stain at one end and a narrower, dark stain at the other.

Based on the appearance of those initial fossil preparations, the first restoration made in 1977 presented us with an animal walking along the bottom of the seafloor on spiny stilts, waving seven dorsal tentacles from its back. The "tentacles" seemed to have a mouth at each tip. These were believed to be feeding aids. You can easily see why Hallucigenia got its curious name.

Recent findings of exceptionally well preserved specimens of an animal closely related to Hallucigenia from the Early Cambrian Chengjiang Fauna of China show us there is a second set of "tentacles" paired with the first, each tipped with a set of claws. This made much more sense. The first fossils were mistakenly reconstructed upside-down! The spines were not used for walking, they were born on the back of animal and may have been used to protect it from predators. The paired, clawed "tentacles" were the real walking legs!
This is one of many examples showing how new research and discoveries, building on the work of previous scientists, increase our understanding of the fossil record.